For the ballistic protection of living beings, articles and devices, in particular buildings or vehicles, safety steels are used. In order to obtain a ballistic protective effect which is as good as possible, the safety steels used here have, in addition to strength which is as high as possible, toughness which is as high as possible combined with hardness which is as high as possible. High hardness of the steels used affords high penetration resistance against a ballistic action and causes for example expanding of a projectile. This allows the penetration depth into the material to be reduced. At the same time, high toughness allows a large amount of energy of the ballistic action to be absorbed in the material. In addition, a material of this type offers high resistance to an undesirable cracking of the material. Generally, hardness and toughness of the material counteract each other; thus, a material having very high hardness, for example, usually tends to be brittle. Materials having high toughness do not, on the other hand, have very high hardnesses. Although the addition of expensive alloy elements, such as for example nickel, molybdenum, chromium or cobalt, allows a very good compromise to be found between toughness and hardness, the alloying and manufacturing costs are nevertheless very high. In addition, care must be taken to ensure that the materials remain reshapable, so that they can be used accordingly.
In order to provide a much more economical solution, composite materials consisting of two different steel alloys are known in the prior art, for example from German Patent specification DE 29 21 854 C1. The first, outer steel alloy layer consists for example of a steel alloy having a carbon content (C content) of from 0.35 to 0.7% by weight, a Si content of from 0.10 to 0.70% by weight, a Mn content of from 0.5 to 1% by weight, P and S each being less than 0.02% by weight, Cr 1.3 to 2.6% by weight, Ni 0.2 to 3.6% by weight, Mo 0.4 to 0.7% by weight and V 0.04 to 0.3% by weight, the remainder being Fe. This outer layer, facing the firing side, is to have particularly high hardness. Together with the steel alloy layer which is arranged therebelow and has an alloy composition of less than 0.15% by weight of C, 0.15 to 0.35% by weight of Si, 0.85 to 1.6% by weight of Mn, P and S each being less than 0.02% by weight, 0.5 to 0.8% by weight of Ni and 0.20 to 0.40% by weight of Al, the remainder being Fe, which steel alloy layer is tougher and softer, improved ballistic protection is obtained. Although the two-layer composite material has provided a marked improvement over a one-layer material with regard to a more economical ballistic protective effect, there is nevertheless an invariable need to improve the ballistic protective effect, the thickness remaining constant or being reduced, in order to attain a reduction in weight, for example in the armor plating of vehicles.